Definition
Plain language
A small puzzle a computer must solve to prove it spent some effort, used to make spamming a system expensive.
As stated in the literature
A computational puzzle that is cheap to verify but costly to produce, used as an anti-spam registration gate so a single legitimate agent is admitted easily while a spam farm faces prohibitive aggregate cost.
Why it matters: It makes spamming or flooding a system costly while letting genuine users in easily, raising the price of abuse without punishing legitimate use.
For example, a site can require each new account to solve a small puzzle that takes a second for one real user but becomes ruinously expensive for someone trying to create a million fake accounts.
Heard on the show
“You register by solving a little cryptographic puzzle — a proof-of-work thing that's cheap for one agent but expensive for a spam farm — and then you're loose in the arena.”Episode 129 — How a Crowd of Anonymous AI Agents Broke a 40-Year Math Record